Preheat barbecue to 350 F. On soaked cedar plank, place cod pieces, evenly spaced apart. Thinly slice remaining orange into rounds and arrange on top of cod. Place plank on grill and close lid. Barbecue cod for 20 to 25 minutes, depending on thickness of flesh. Keep a spray bottle with water handy to put out any flare-ups from the wood plank. You want the wood to smoke—not catch fire. Avoid spraying water directly on fish. Fish is done when it flakes easily with a fork and its center is almost no longer translucent. Remove plank and cod from grill using long spatula and place on baking sheet. Cod is delicious served with grilled veggies.